1. Field of the Invention
The present invention generally relates to an optical recording method and apparatus for an optical storage medium, and more particularly to an optical recording method and apparatus that achieves the recording of a high-density optical storage medium at a high recording speed above a basic recording speed by setting the recording pulse pattern so as to match with either a constant-angular-velocity recording process or a variable-linear-velocity recording process.
2. Description of the Related Art
As disclosed in Japanese Laid-Open Patent Application No.11-232652, an optical recording method is known, and this optical recording method is aimed at achieving appropriate recording of an optical storage medium at a high recording speed above a basic recording speed. In the optical recording method of the above document, the recording pulse pattern is set, when performing the high-speed recording, such that the width of a top recording pulse and the width of a following recording pulse are respectively larger than those of the recording pulse pattern that is set when performing the basic-speed recording. Alternatively, when performing the high-speed recording, the recording light power is set such that it is larger than the recording light power that is set when performing the basic speed recording.
Today, in order to achieve speedy recording of CD-R (compact disk recordable) and CD-RW (compact disk rewritable) media, the recording of these media is performed at not only the basic recording speed but also the double or quadruple recording speed. There is an increasing demand for achieving high-speed recording of DVD media in order to shorten the recording time of DVD media that are high-density optical storage media. For example, consideration is given to achieving high-speed recording of a DVD-R by performing the CAV (constant angular velocity) recording or the ZCAV (z-constant angular velocity) recording. In such a case, if the basic recording speed is used at the innermost track of the optical disk, a 2.5-times higher recording speed is needed at the outermost track of the optical disk. The recording linear velocity when performing the constant angular velocity recording depends on the radius of the recording position or the track of the optical disk.
Generally, if the recording pulsewidth is solely controlled in accordance with the recording linear velocity so as to cover a required range of the recording linear velocity (e.g., the range between the basic recording speed and the 2.5-times higher recording speed), the effect to improve the jitter is apt to become inadequate. In order to increase the effect of the jitter improvement and match with the required range of the recording linear velocity, it is necessary to appropriately control not only the recording pulsewidth but also the recording power in accordance with the recording linear velocity or the recording position of the disk.
It is desirable that the control of the recording pulsewidth can be performed as simply as possible when controlling both the recording pulsewidth and the recording power in accordance with the recording linear velocity. If many control parameters must be controlled or the setting of control parameters is complicated, small errors of the individual control parameters in combination will be significant, which causes the deterioration of the jitter that is unexpectedly serious.
The conventional optical recording method of the above document utilizes a multi-pulse recording scheme in which two or more sequences of recording pulses, each sequence including multiple pulses, are used. To record one of two or more kinds of marks having different lengths on the storage medium, a corresponding one of the two or more sequences of recording pulses is selected. The thermal interference of the multiple pulses greatly depends on the recording linear velocity. Hence, it is necessary for the conventional optical recording method of the above document to individually control the pulsewidths of the respective pulses included in the selected sequence in a complicated manner. It is necessary to determine a different amount of correction of the recording pulsewidth for each of the different kinds of marks in accordance with the recording linear velocity or the recording position. Further, it is necessary to determine a specific amount of correction of the recording pulsewidth for a mark that is interposed between the preceding space and the following space with certain lengths.
Therefore, when the recording pulsewidth is controlled in accordance with the recording linear velocity or the recording position, there is a problem in that many control parameters must be controlled or the setting of control parameters is complicated. For example, the amount of correction of the recording pulsewidth allocated for one of different kinds of marks is considerably different from the amount of correction of the recording pulsewidth allocated for another of the different kinds of marks. In the control of the recording pulsewidth, the correction of the recording pulsewidth must be performed for all of the marks to be recorded on the storage medium.
In addition, it is desirable that each control parameter can be expressed as a continuous linear function of the recording position or the recording linear velocity. If the control parameter is not expressed as a continuous linear function, the optimum control parameter does not have a constant value for an error of the recording linear velocity (or the recording position), it is rapidly fluctuated, and the deterioration of the jitter is not prevented sufficiently. If the control parameter is expressed as a discontinuous function, the optimum control parameter is rapidly fluctuated for an error of the recording linear velocity, and the deterioration of the jitter is not prevented sufficiently.
Specifically, suppose that a high-speed recording of a DVD-R is achieved when performing the CAV recording process. As described above, if the basic recording speed is used at the innermost track of the disk, the 2.5-times higher recording speed is created at the outermost track of the disk.
The standard of DVD-R specifications specifies that the (n−2) multi-pulse recording scheme be used when performing the recording at the basic recording speed. For example, in the (n−2) multi-pulse recording scheme, a recording pulse waveform for a 3T data consists of a single (=3−2) recording pulse, a recording pulse waveform for a 4T data consists of two (=4−2) recording pulses, and a recording pulse waveform for a 6T data consists of four (=6−2) recording pulses. FIG. 9 shows the recording pulse waveform for the 6T data when the (n−2) multi-pulse recording scheme is used.
In FIG. 9, “T” indicates a unit length corresponding to a channel bit, “TSFP” indicates a time duration from the rising edge of the 6T data to the rising edge of the top pulse, “TEFP” indicates a time duration from the rising edge of the 6T data to the trailing edge of the top pulse, “TSMP” indicates a time duration from one third of the 6T data to the rising edge of the following pulse, “TEMP” indicates a time duration from one third of the 6T data to the trailing edge of the following pulse, “TSLP” indicates a time duration from two thirds of the 6T data to the rising edge of the last pulse, and “TELP” indicates a time duration from two thirds of the 6T data to the trailing edge of the last pulse.
However, if the (n−2) multi-pulse recording scheme is used at the 2.5-times higher recording speed, the energy of the recording light needed to record short marks at the outer tracks of the disk will be insufficient. In the above case, it is difficult to obtain the recording characteristics (in particular, the recording of short marks on the disk) that are equivalent to those obtained at the basic recording speed. To eliminate the problem, it is desired to selectively use the (n−1) multi-pulse recording scheme, instead of the (n−2) multi-pulse recording scheme, when the recording is performed at the 2.5-times higher recording speed. If the (n−1) multi-pulse recording scheme is selectively used at the 2.5-times higher recording speed, the recording characteristics that are equivalent to those obtained at the basic recording speed can be obtained. For example, in the (n−1) multi-pulse recording scheme, a recording pulse waveform for a 3T data consists of two (=3−1) recording pulses, and a recording pulse waveform for a 4T data consists of three (=4−1) recording pulses. FIG. 10 shows a recording pulse waveform for a 6T data when the (n−1) multi-pulse recording scheme is used. The recording pulse waveform shown in FIG. 10 consists of five recording pulses.
The notations of FIG. 10 are essentially the same as those of FIG. 9 except that, in FIG. 10, “TSLP” indicates a time duration from five sixths of the 6T data to the rising edge of the last pulse, and “TELP” indicates a time duration from five sixths of the 6T data to the trailing edge of the last pulse.
As described above, when the recording pulsewidth is controlled in accordance with the recording position of the disk during the CAV recording process, it is necessary to switch, at a certain intermediate position of the disk, between the (n−2) multi-pulse recording scheme and the (n−1) multi-pulse recording scheme, in order to avoid the insufficiency of the recording light energy at the outer tracks of the disk. In addition, for the ease of the control parameter setting and for the improvement of the jitter characteristics, it is necessary to perform continuously the switching from the (n−2) multi-pulse recording scheme to the (n−1) multi-pulse recording scheme in accordance with the recording position or the recording linear velocity.
One conceivable method of the continuous switching is that the recording pulsewidth of the last pulse within the multi-pulse waveform is controlled in accordance with the recording position of the disk, such that the rising edge of the last pulse approaches the trailing edge of the last one of the middle pulses within the multi-pulse waveform. Alternatively, the recording pulsewidth of the top pulse within the multi-pulse waveform may be controlled in a similar manner such that the trailing edge of the top pulse approaches the rising edge of the first one of the middle pulses within the multi-pulse waveform. However, the range of the recording pulsewidth that can be adjusted in the multi-pulse waveform is limited. It is very difficult to make the time duration between the rising edge of the last pulse and the trailing edge of the last middle pulse within the multi-pulse waveform infinitely approach zero. Hence, it is very difficult to make the above method of the continuous switching feasible.
Another conceivable method of the continuous switching is that the recording pulsewidth of the last pulse within the multi-pulse waveform is controlled in accordance with the recording position of the disk, such that the rising edge of the last pulse approaches the trailing edge of the last one of the middle pulses within the multi-pulse waveform while the pulsewidth of the last pulse is reduced. Alternatively, the recording pulsewidth of the top pulse within the multi-pulse waveform may be controlled in a similar manner such that the trailing edge of the top pulse approaches the rising edge of the first one of the middle pulses within the multi-pulse waveform while the pulsewidth of the top pulse is reduced. However, it is very difficult to make the pulsewidth of the last pulse (or the top pulse) within the multi-pulse waveform infinitely approach zero. Hence, it is very difficult to make the above method of the continuous switching feasible.